//背景图片
bg-image($url)
    background-image: url($url + "@2x.png");
    @media (min-device-pixel-ratio: 3),(-webkit-min-device-pixel-ratio: 3) 
            background-image: url($url + "@3x.png");
no-wrap()
    text-overflow: ellipsis
    overflow :hidden
    white-space: nowrap
extend-click()
    position: relative
    &:before
        content: ""
        position:absolute
        left: -10px
        right: -10px
        top: -10px
        bottom: -10px